Most vehicles are powered by reciprocating piston engines and must face widely varying load conditions such as quick accelerations, highway cruising, city traffic and idling. As a rule, vehicle engines are sized in relation to the most demanding requirements, namely acceleration and climbs, which represent less than 5% of the engine usage. At other than these precited operating conditions, say a 100 horsepower engine could well be replaced with a 50 or even a 25 horsepower engine, the efficiency of which would be far greater than that of an oversized 100 horsepower engine. It will be even more interesting if the 100 horsepower engine could be turned out as a 10 Hp machine during idling. The range of horsepower requirements similar to the ones mentioned above have been arrived at after extensive studies and produced as standards, one of these being the Los Angeles "LA-4 Synthetic driving cycle" and another one being the "Pittsburg Cycle".
The fact is that engines are efficient when producing their desing horsepower with piston speeds close to 1000 feet per minute, maximum efficiency occurs at close to these piston speeds at approximately 80% maximum capacity. These operating criteria are related to thermodynamics. The use of gearboxes merely serves the purpose of adapting the engine to low speed loads by making the engine run faster, thus producing many more useless reciprocating movements. Hence, outside ideal operating conditions, the machine performance and efficiencies deteriorate, specially at reduced speed whereas combustion is poor; this applies very much to spark ignition engines and also, to a lesser extent, to the diesel engines.
A few patents embodying means to vary piston speed have been proposed, as in Reese U.S. Pat. No. 1,191,827 and Renshaw U.S. Pat. No. 3,301,244, but the models of the abovementioned patents show high friction losses and require extensive construction without possible speed evenness. Variable stroke engines have been proposed to improve engine performance, and other mechanisms have been proposed in order to change the waveshape of the piston travel time as in Indech U.S. Pat. No. 4,211,190 and in Schinke U.S. Pat. No. 1,873,908 and in Mederer U.S. Pat. No. 4,437,438, but no efficient device has been proposed to eliminate some of the useless piston travels when an engine is running at low power requirements. Moreover, when comparing to the present invention, no such arrangement of readily available multi-horsepower capacity through optional variation of piston movement has been shown in any of the precited Patents documents and the I.C. engine with conventional piston/crankshaft arrangement is still the prevailing prime mover around.